I noticed the blinking of the plug symbol is asymmetric (3 secs on, 1
sec off). Is that intentional?

Having looked at the different styles to present battery level and
charging state, I think a steady battery symbol (or, upon config
option, a number) plus a flashing charger plug is the most informative
since the actual battery level is a good indicator of the progress of
the charging process.

My suggestion would be to make this style of display available
elsewhere as well, and to add a configuration option "charging
indicator" with values "battery symbol" and "plug symbol".